In tank containers, the connection between tie tank and the container frame is often done by means of saddle elements which are welded to the tank, on the one hand, and to diagonal struts inserted in the container frame, on the other hand. Examples of this type of tank saddle structure are found in U.S. Pat. No. 4,593,832, European Patent Application Publication No. 0,425,190 and U.K. Patent No. 1,468,665.
In a further design known from U.S. Pat. No. 4,421,243, which also requires diagonal struts provided in the frame, the cylindrical tank envelope extends continually from one end frame to the other and is butt welded to the respective diagonal struts, with the tank bottoms being fitted into the tank envelope.
A disadvantage of this design resides in the fact that the diagonal struts required in both end frames increase the amount of material used, the manufacture expenditure and the tare weight of the tank container.
Diagonal struts in an end frame have the further disadvantage that they do not permit a simple mounting of a ladder which is to be provided there. Instead, since the ladder is required to be disposed within the container length defined by the end frames, it must be made of specially shaped individual parts to be fir into the spaces left free by the diagonal struts and outer frame members. Moreover, diagonal struts crossing the area of the ladder impair the usability and operational safety of the ladder.
U.S Pat. No. 4,307,812 discloses another saddle structure which in practice is often employed with tank containers. In this structure, the tank in the region of its bottom ends is connected to the respective end frame by means of four saddle pieces each of which is formed as a shell element shaped from a sheet metal blank, with one edge welded to a reinforcing ring surrounding the tank and opposite edges welded to the transverse bars and corner struts of the end frame. If such shell-type saddles are used, no diagonal struts are necessary in the end frames. One difficulty, however, resides in the fact that the shell-type saddles due to their specific shape are expensive to manufacture and require different forming for every tank diameter.
European Patent Specification No. 0,654,421 discloses a tank container having a pair of end frames and a substantially cylindrical tank, the curved bottoms of which are connected to each of the end frames via a saddle structure which comprises an end ring mounted on the tank bottom and a saddle ring connecting the end ring to the end frame. This type of connection between the tank and the container frames, in which the end frames may be free of diagonal elements, is suitable for small and medium size containers.